Occurrence of bacteria in the primary oocytes of vesicomyid clam Calyptogena soyoae

Abstract

Intracellular procaryotic cells were consistently found in TEM observations of primary oocytes and follicle cells of the deep-sea seepage clam Calyptogena soyoae . These bacteria resembled gill endosymbionts in the following 3 points: dimensions and general outline, occurrence of electron-transparent vacuoles in the periplasm, and occurrence of electron-dense materials in the periplasm. Eggs which harbored bacteria were all in the vitellogenic stage. This finding suggests some restricted time schedule of the entry of bacteria into oocytes. It is hypothesized that these bacteria represent transmission stage of gill symbionts, and continuum of the symbiosis is maintained by maternal inheritance through egg infection.